title: A cation-pi interaction in the binding site of the glycine receptor is mediated by a phenylalanine residue.
abstract: Cys-loop receptor binding sites characteristically contain many aromatic amino acids. In nicotinic ACh and 5-HT3 receptors, a Trp residue forms a cation-pi interaction with the agonist, whereas in GABA(A) receptors, a Tyr performs this role. The glycine receptor binding site, however, contains predominantly Phe residues. Homology models suggest that two of these Phe side chains, Phe159 and Phe207, and possibly a third, Phe63, are positioned such that they could contribute to a cation-pi interaction with the primary amine of glycine. Here, we test this hypothesis by incorporation of a series of fluorinated Phe derivatives using unnatural amino acid mutagenesis. The data reveal a clear correlation between the glycine EC(50) value and the cation-pi binding ability of the fluorinated Phe derivatives at position 159, but not at positions 207 or 63, indicating a single cation-pi interaction between glycine and Phe159. The data thus provide an anchor point for locating glycine in its binding site, and demonstrate for the first time a cation-pi interaction between Phe and a neurotransmitter.
authors.affiliation: School of Biomedical Sciences and Queensland Brain Institute, University of Queensland, Brisbane, Queensland 4072, Australia.
authors.forename: Stephan A
authors.initials: SA
authors.lastname: Pless
authors.forename: Kat S
authors.initials: KS
authors.lastname: Millen
authors.forename: Ariele P
authors.initials: AP
authors.lastname: Hanek
authors.forename: Joseph W
authors.initials: JW
authors.lastname: Lynch
authors.forename: Henry A
authors.initials: HA
authors.lastname: Lester
authors.forename: Sarah C R
authors.initials: SC
authors.lastname: Lummis
authors.forename: Dennis A
authors.initials: DA
authors.lastname: Dougherty
mesh_terms: D024322:Amino Acids, Aromatic / Q000737:chemistry; D000818:Animals; D001665:Binding Sites / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D002412:Cations / Q000737:chemistry*; D005998:Glycine; D006801:Humans; D008845:Microinjections; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed / Q000379:methods; D009865:Oocytes; D010649:Phenylalanine / Q000378:metabolism*; D011485:Protein Binding / Q000235:genetics / Q000502:physiology; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D011869:Radioligand Assay; D018009:Receptors, Glycine / Q000235:genetics*; D013329:Structure-Activity Relationship; D014982:Xenopus laevis
chemical_list: D024322:Amino Acids, Aromatic; D002412:Cations; D018009:Receptors, Glycine; D010649:Phenylalanine; D005998:Glycine